Date: Tue, 30 Jul 2013 16:16:58 +0200 From: Dimitry Andric <dim@freebsd.org> To: Matthew Fleming <mdf@freebsd.org> Cc: "svn-src-head@FreeBSD.org" <svn-src-head@freebsd.org>, "svn-src-all@FreeBSD.org" <svn-src-all@freebsd.org>, "src-committers@FreeBSD.org" <src-committers@freebsd.org> Subject: Re: svn commit: r253802 - head/contrib/llvm/tools/clang/lib/Headers Message-ID: <2DE35C45-B110-4D93-BFA7-542A3D1EE902@freebsd.org> In-Reply-To: <CAMBSHm8xDvWsKJiLAzPF8azMKLHq3WWWQ3X1d6-6nJSAppux9Q@mail.gmail.com> References: <201307301233.r6UCXLT8012177@svn.freebsd.org> <CAMBSHm8xDvWsKJiLAzPF8azMKLHq3WWWQ3X1d6-6nJSAppux9Q@mail.gmail.com>
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On Jul 30, 2013, at 16:09, Matthew Fleming <mdf@freebsd.org> wrote: > On Tue, Jul 30, 2013 at 5:33 AM, Dimitry Andric <dim@freebsd.org> = wrote: > Author: dim > Date: Tue Jul 30 12:33:21 2013 > New Revision: 253802 > URL: http://svnweb.freebsd.org/changeset/base/253802 >=20 > Log: > Pull in r186696 from upstream clang trunk: >=20 > This patch implements __get_cpuid_max() as an inline and __cpuid() > and __cpuid_count() as macros to be compatible with GCC's cpuid.h. > It also adds bit_<foo> constants for the various feature bits as > described in version 039 (May 2011) of Intel's SDM Volume 2 in the > description of the CPUID instruction. The list of bit_<foo> > constants is a bit exhaustive (GCC doesn't do near this many). = More > bits could be added from a newer version of SDM if desired. ... > +/* PIC on i386 uses %ebx, so preserve it. */ > +#if __i386__ > +#define __cpuid(__level, __eax, __ebx, __ecx, __edx) \ > + __asm(" pushl %%ebx\n" \ > + " cpuid\n" \ > + " mov %%ebx,%1\n" \ > + " popl %%ebx" \ ... > PIC mode on amd64 also uses %ebx. The difference is that FreeBSD = makefiles set -fPIC for i386 kernel compile but not amd64. Locally we = use -fPIC for amd64 (it was added 6 years ago to our environment because = it gave better kernel debugging). >=20 > Anyways, is there some way to detect PIC mode and use that to decide = whether to use %ebx for the cpuid instruction, rather than using i386? Upstream gcc checks this with: #if defined(__i386__) && defined(__PIC__) ... #elif defined(__x86_64__) && (defined(__code_model_medium__) || = defined(__code_model_large__)) && defined(__PIC__) ... and it exchanges ebx or rbx with %k1 or %q1, respectively, instead of = push/pop. That might be a little more efficient. I guess the defined(__PIC__) should be enough for us, in most cases. = The code_model stuff is for x32 support, which we do not have yet. -Dimitry
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